最终变量和非最终变量之间的快速差异最终让与非最终让 [英] swift difference between final var and non-final var | final let and non-final let

问题描述

最终变量和非最终变量有什么区别:

What's difference between final variables and non-final variables :

var someVar = 5
final var someFinalVar = 5

和

let someLet = 5
final let someFinalLet = 5

推荐答案

final修饰符在

最终

将此修饰符应用于类或类的属性，方法或下标成员.应用于类别以指示该类别不能被子类别化.它应用于类的属性，方法或下标，以指示类成员不能在任何子类中被覆盖.

Apply this modifier to a class or to a property, method, or subscript member of a class. It’s applied to a class to indicate that the class can’t be subclassed. It’s applied to a property, method, or subscript of a class to indicate that a class member can’t be overridden in any subclass.

这意味着没有final，我们可以写:

This means without final we can write:

class A {
    var x: Int {return 5}
}
class B : A {
    override var x: Int {return 3}
}
var b = B()
assert(b.x == 3)

但是如果我们在类A

class A {
    final var x: Int {return 5}
}
class B : A {
    // COMPILER ERROR
    override var x: Int {return 3}
}

然后发生这种情况:

$ swift final.swift 
final.swift:6:18: error: var overrides a 'final' var
    override var x: Int {return 3}
             ^
final.swift:2:15: note: overridden declaration is here
    final var x: Int {return 5}

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